Educational reference only. Not medical advice. Consult a healthcare provider before starting any protocol.
IGF-1 LR3
Long R3 Insulin-like Growth Factor-1
What it is
A modified analog of human IGF-1 in which glutamic acid at position 3 is replaced with arginine and a 13-amino-acid extension is added to the N-terminus. These modifications dramatically reduce binding affinity for all six IGF binding proteins (IGFBPs), resulting in a much higher free bioactive fraction compared to native IGF-1. IGF-1 LR3 is approximately 3× more potent than native IGF-1 in cell proliferation assays and activates the PI3K/Akt/mTOR and MAPK/ERK pathways. It has been studied in animal models for effects on organ growth, intestinal epithelial proliferation, and protein anabolism. No human clinical trials have been conducted with this specific compound. The FDA-approved recombinant IGF-1 product (mecasermin/Increlex) uses the native 70-amino-acid sequence, not the LR3 variant.
Community-reported ranges
Ranges sourced from community forums and published preclinical literature. Not dosing guidance. Dose units are mcg/day.
Reported dose range
20–100 mcg
Estimated half-life
~20-30 hours (estimated)
Source: inferred from reduced IGFBP binding and in vitro persistence data; no formal human PK study exists
Reported cycle length
4–6 weeks on
4-6 weeks off
Route
subcutaneous, intramuscular
Common vial sizes
1mg
Reported timing
Post-workout or AM
Reported frequency
1x daily
Frequently discussed alongside
Based on community forum discussions. Not a recommendation to combine compounds.
IGF-1 DES
The two primary IGF-1 analogs discussed in community contexts, often compared for systemic vs. site-specific protocols
MK-677 (Ibutamoren)
Discussed as a GH secretagogue stack to raise endogenous GH alongside exogenous IGF-1
CJC-1295
Often discussed in GH/IGF-1 axis stacking protocols with GHRH analogs
Published research
Animal studies have examined IGF-1 LR3 across models including intestinal epithelial proliferation in rats (Steeb et al., 1995), organ growth in guinea pigs and fetal sheep, and amyloid plaque remodeling in Alzheimer's mouse models (2024). The compound's reduced IGFBP binding and extended bioactivity relative to native IGF-1 are well-characterized in vitro. No peer-reviewed human clinical trials have been conducted with IGF-1 LR3 as of March 2026. All human clinical data for the IGF-1 class uses native-sequence recombinant IGF-1 (mecasermin). Community dosing ranges are extrapolated from animal data and are not clinically validated.
Reported side effects
From community self-reports. Not from controlled studies.
The most significant acute risk studied in the IGF-1 class is hypoglycemia. Animal studies have shown organ enlargement (gut, kidney, spleen, adrenal) with LR3 infusion, and one rat study observed increased mammary tumor growth. Community users have reported joint pain, water retention, headaches, nausea, injection site reactions, and gut distension at higher doses. Systematic human safety data does not exist for this compound.
Regulatory status
FDA (United States)
Not approved. Placed on FDA Category 2 bulk drug substance list (September 2023) — cannot be compounded by 503A or 503B pharmacies. Potential reclassification under review as of early 2026 but not yet finalized.
Health Canada
Not authorized as a therapeutic product. No DIN assigned. Health Canada has conducted seizures of unauthorized injectable peptide products from online vendors.
WADA (Competitive Athletes)
Prohibited at all times under S2.3 — Growth Factors and Growth Factor Modulators. Classified as a non-specified substance. WADA has funded LC-ESI-MS/MS detection methods specifically for LR3-IGF-1 in athlete plasma.
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